Optical recording medium, information recording method, and information reproducing method

ABSTRACT

According to one embodiment, an optical recording medium is provided in which interlayer crosstalk is low and in which stable and high-quality recording characteristics can be obtained. To this end, an optical recording medium comprises a first recording part which includes a first recording layer and a first light reflecting layer and which is disposed on a side closer to a light receiving surface, and a second recording part which includes a second recording layer and a second light reflecting layer and which is disposed on a side farther from the light receiving surface, the first recording part and the second recording part being stacked, wherein the thickness of the second light reflecting layer is larger than the thickness of the first light reflecting layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2006-155110, filed Jun. 2, 2006, theentire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

One embodiment of the present invention relates to a recordable opticalrecording medium for recording and playing back information by opticalchanges in the transmittance, reflectance, etc. of a recording layerinduced by the application of a light beam.

2. Description of the Related Art

In an optical recording medium such as a CD-R or a DVD-R using a dyematerial, part of a recording wavelength is optically absorbed in anorganic dye thin film used in a recording layer, and the decompositionof the organic dye thin film and the physical deformation of a recordingfilm are caused by heat generation in the recording layer due to theoptical absorption, thereby achieving signal recording. Development hashitherto been made to increase recording density by reducing thewavelength of recording laser. A certain degree of density enhancementis possible when recent blue laser of about 400 nm is applied, but ithas naturally started to face a limit in recording capacity. There isused a technique of, for example, multiplying the recording layer inorder to achieve higher recording density, and, for example, adual-layer DVD-R has been commercialized. However, for themultiplication of layers, the optical transmittance and opticalabsorptance of the recording layers have to be strictly controlled andthe structure of the disc has to be optimized so that a stablerecording/playback signal can be obtained. However, the techniques forproducing multiple layers out of the dye material have not yet reached apractically adequate level due to technical difficulties. Therefore, theselling prices of such discs are higher than those of single-layerdiscs. Behind such circumstances, there has been reported a disc inwhich the order of forming the recording films in a layer located on afar side when viewed from a light entering surface is reversed to aconventional order in order to improve recording characteristics of themultilayer disc.

For example, Jpn. Pat. Appln. KOKAI Publication No. 2005-339761 suggeststhe introduction of a metal oxide layer between a dye layer and areflecting layer to improve recording/playback characteristics, a dyerecording film needs to be formed on a reflecting film in theconfiguration of a recording layer, and a new protective layer needs tobe created to prevent the interference between a bonding resin used inan intermediate layer and the dye material. A process of manufacturingthe conventional single-layer disc using the dye material is not easilyadapted to the multilayer disc, and production costs can be increased ifhigh mass productivity and production yield are to be maintained becausestrict management of production is demanded.

Furthermore, when the recording layers have the multilayer structure,the quality of a recording signal easily changes due to a slightdifference of optical characteristics of the materials of the respectivelayers, mutual optical interference, etc., so that there is apossibility that the margin of the designing of the configurations ofthe recording layers is decreased in the case where crosstalk betweenthe recording layers is controlled. The technique of the multiplicationof layers is fundamental to achieve the high density recording, but noclear designing guidance is provided in the present situation, and noreport has been found regarding a method of controlling the interlayercrosstalk due to the multiplication of layers.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various feature of theinvention will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the invention and not to limit the scope of theinvention.

FIG. 1 is an exemplary diagram explaining an example of theconfiguration of a multilayer optical disc according to one embodimentof this invention;

FIG. 2 is an exemplary diagram showing a concrete example of a metalcomplex portion of an organic material for a recording layer;

FIG. 3 is an exemplary diagram showing one example of a dye portion ofthe organic material for the recording layer;

FIG. 4 is an exemplary diagram explaining an example of setting generalparameters in a recordable information storage medium;

FIG. 5 is an exemplary flowchart explaining a recording method using theoptical disc according to the one embodiment of this invention;

FIG. 6 is an exemplary flowchart explaining a reproducing method usingthe optical disc according to the one embodiment of this invention;

FIG. 7 is an exemplary diagram explaining an example of the layout ofphysical sectors in the optical disc in FIG. 1;

FIG. 8 is an exemplary diagram explaining an example of theconfiguration of a lead-in area in the optical disc in FIG. 1;

FIG. 9 is an exemplary diagram explaining an example of theconfiguration of a control data zone in FIG. 8;

FIG. 10 is an exemplary diagram explaining the example of theconfiguration in FIG. 9;

FIG. 11 is an exemplary diagram explaining one example of physicalformat information in FIG. 10;

FIG. 12 is an exemplary diagram explaining one example of data areaallocation in the physical format information in FIG. 11;

FIG. 13 is an exemplary diagram explaining an example of theconfiguration of a part (associated with L0) of the physical formatinformation in FIG. 10;

FIG. 14 is an exemplary diagram explaining an example of theconfiguration of another part (associated with L1) of the physicalformat information in FIG. 10;

FIG. 15 is an exemplary diagram explaining an example of waveforms(write strategy) of recording pulses;

FIG. 16 is an exemplary diagram explaining the formation of a burstcutting area (BCA) on an L1 layer of a recordable single-sidedmultilayer (dual-layer) optical disc according to the one embodiment ofthis invention;

FIGS. 17A and 17B are exemplary diagrams explaining an example ofcontents of BCA record recorded in the BCA in FIG. 16;

FIG. 18 is an exemplary diagram explaining an example of theconfiguration of a device for recording specific information includingthe BCA record, etc. in FIGS. 17A and 17B in the BCA;

FIG. 19 is an exemplary flowchart explaining one example of a procedurefor recording the specific information (the BCA record, etc.) in an L1layer of the recordable single-sided multilayer (dual-layer) opticaldisc in FIG. 16;

FIG. 20 is an exemplary flowchart explaining one example of a procedurefor reproducing the specific information (the BCA record, etc.) from theL1 layer of the recordable single-sided multilayer (dual-layer) opticaldisc in FIG. 16; and

FIG. 21 is an exemplary diagram explaining an example of a process ofmanufacturing the recordable single-sided dual-layer optical discaccording to the one embodiment of this invention.

DETAILED DESCRIPTION

Various embodiments according to the invention will be describedhereinafter with reference to the accompanying drawings.

When information is recorded in an optical recording medium having aplurality of (e.g., two) recording layers, power of a light beam whichhas entered from a first recording layer (L0) is divided into two dueto, for example, the presence of a light reflecting layer included inthe first recording layer, and allocated to recording/playback for thefirst recording layer (L0) and recording/playback for a second recordinglayer (L1). Therefore, the light beam reduced by half has to beefficiently reflected in a light reflecting layer included in the secondrecording layer (L1). Thus, a high-reflectance material such as Ag or anAg alloy is used to increase the reflectance. However, if the thicknessof the light reflecting layer of the second recording layer (L1) isincreased, the amount of reflection is increased, which increases anoptical interference between the first recording layer (L0) and arecording signal. There is therefore a problem of significantdeterioration in the quality of a recording/playback signal because ofincreased crosstalk between the first recording layer (L0) and thesecond recording layer (L1).

The embodiments of this invention solve such problems in examiningrecording characteristics of an optical recording medium having aplurality of (e.g., two) recording layers.

That is, one challenge of the embodiments of this invention is toprovide an optical recording medium in which interlayer crosstalk is lowand in which stable and high-quality recording characteristics can beobtained.

In the optical recording medium according to one embodiment of thisinvention, the material of the reflecting film and the thickness of thereflecting film are adjusted to optimize the reflectance of the lightreflecting layer included in the second recording layer, such that thecrosstalk between the first recording layer and the second recordinglayer is reduced, and the stable and high-quality recordingcharacteristics are obtained. In other words, in the optical recordingmedium according to one embodiment of this invention having the firstrecording layer and the second recording layer in which information canbe recorded/played back by light, the material and the thickness of thereflecting film of a light reflecting layer included in the secondrecording layer are adjusted.

Thus, in the multilayer recordable information recording medium, theoccurrence of the interlayer crosstalk due to light applied to layersother than a desired layer is prevented when a laser beam is convergedon the desired layer.

FIG. 1 is a diagram explaining an example of the configuration of anoptical disc (a recordable single-sided dual-layer optical disc as aconcrete example) 100 according to the one embodiment. As illustrated in(a) and (b) in FIG. 1, this optical disc 100 comprises a transparentresin substrate 101 formed of a synthetic resin material such aspolycarbonate (PC) to have a disc shape. A groove is concentrically orspirally formed in this transparent resin substrate 101. The transparentresin substrate 101 can be manufactured by injection molding using astamper.

Here, an organic dye recording layer 105 and a light semi-transmissivereflecting layer 106 of a first layer (L0) are stacked in order on thetransparent resin substrate 101 formed of, for example, polycarbonateand having a thickness of 0.59 mm, the top of which is spin-coated witha photopolymer (2P resin) 104. Then, the shape of a groove of a secondlayer (L1) is transferred onto the top of the photopolymer 104, and anorganic dye recording layer 107 and a reflecting film 108 made of, forexample, silver or a silver alloy are stacked thereon in order. To thestack of the recording layers of the L0 and L1, another transparentresin substrate (or a dummy substrate) 102 having a thickness of 0.59 mmis bonded via a UV curing resin (adhesive layer) 103. The organic dyerecording film (the recording layers 105 and 107) has a dual-layerstructure in which the semi-transmissive reflecting layer 106 and theintermediate layer 104 are interposed in between. A total thickness ofthe laminated optical disc finished in this manner is about 1.2 mm.

Here, on the transparent resin substrate 101, a spiral groove having,for example, a track pitch of 0.4 μm and a depth of 60 nm is formed (inthe respective layers L0 and L1). This groove has a wobble, and addressinformation is recorded on this wobble. The recording layers 105 and 107containing an organic dye are formed on the transparent resin substrate101 to fill the groove.

To form the recording layers 105 and 107, an organic dye can be used inwhich its maximum absorption wavelength region is shifted to a longerwaveform side than a recording wavelength (e.g., 405 nm). Moreover,absorption is not vanished in a recording wavelength region, and itslong wavelength region (e.g., 450 nm to 600 nm) is designed to alsoabsorb a significant amount of light.

The organic dye (a concrete example of which will be described later) isdissolved in a solvent and liquefied, and can thus be easily applied tothe surface of the transparent resin substrate by a spin coat method. Inthis case, the rate of dilution with the solvent and the number ofrevolutions during the spin coat are controlled so that the filmthickness can be managed with high accuracy.

In addition, light reflectance is low when a recording laser beam isfocused on or tracking is performed on a track before the recording ofinformation. Then, the decomposition and reaction of the dye are inducedby the laser beam, and light reflectance in a recording mark portionincreases due to a decrease in the optical absorptance of the dye. Thus,so-called Low-to-High (or L to H) characteristics are achieved whereinthe light reflectance in the recording mark portion formed by theapplication of the laser beam becomes higher than light reflectancebefore the application of the laser beam.

In this one embodiment, physical formats applied to the L0 layer and theL1 layer present on the transparent resin substrate 101 and thephotopolymer (2P resin) 104 are as described below. That is, generalparameters of the recordable single-sided dual-layer disc are about thesame as general parameters of a single-layer disc, but are different inthe following points. A recording capacity available to a user is 30 GB,the inside radius of a data area is 24.6 mm in the layer 0 (L0 layer)and 24.7 mm in the layer 1 (L1 layer), and the outside radius of thedata area is 58.1 mm (both in the layer 0 and the layer 1).

In the optical disc 100 in FIG. 1( a), a system lead-in area SLAincludes a control data section as illustrated in FIG. 1( c), and thiscontrol data section contains parameters regarding the recording ofrecording power (peak power), bias power, etc. as part of physicalformat information, etc., separately for the L0 and L1.

Furthermore, mark/space recording is carried out in a track within adata area DA of the optical disc 100 by laser containing predeterminedrecording power (peak power) and bias power, as illustrated in FIG. 1(d). Owing to this mark/space recording, object data (VOB, etc.) for, forexample, a high-definition TV broadcast program, and its managementinformation (VMG) are recorded on the tracks (of the L0 and/or L1)within the data area DA, as illustrated in FIG. 1( e).

Organic dyes that can be used in this one embodiment include, forexample, cyanine dyes, styryl dyes, azo dyes, etc. The cyanine dyes andthe styryl dyes are particularly preferable because they allow easycontrol on their absorptance with respect to a recording wavelength.Moreover, the azo dyes may be used in the form of a single azo compound,or in the form of a complex of one or more molecules of the azo compoundand a metal.

An azo metal complex that can be used in this one embodiment usescobalt, nickel or copper as its central metal M in order to have higherphotostability. However, the central metal M of the azo metal complexthat can be used is not limited to these metals, and may be scandium,yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum,chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron,ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, gold,zinc, cadmium, mercury, etc.

The azo compound has an aromatic ring, and not only the structure of thearomatic ring but also the provision of the aromatic ring with varioussubstituents permits the optimization of recording characteristics,saving characteristics, playback characteristics, etc. The bulkiersubstituents tend to have an improvement in playback light resistance,but also tend to have lower sensitivity in recording, so that theselection of a substituent satisfactory in both of these characteristicsis fundamental. Moreover, this substituent is concerned with thesolubility into a solvent.

Unlike recording mechanisms of conventional dye-based informationrecording media (whose recording laser wavelengths are longer than 620nm), the recording mechanism of short-wavelength laser recording (whoserecording wavelength is, for example, 405 nm) related to thisapplication is not based on physical changes in a substrate and thevolume of a dye film. During playback, the orientation of dye moleculeswithin the recording layers or the conformation in the dye molecules isgradually changed by heat or light due to the application of laserweaker than that during recording to the dye, but the presence of thebulky substituent in the dye molecules is considered to have the effectof preventing such changes from being easily caused. This is why thebulky substituent contributes to the improvement of the playback lightresistance.

The bulky substituent at this point means a substituent composed ofthree or more carbons substituted for the aromatic rings in the dyemolecules, and includes an n-propyl group, an isopropyl group, ann-butyl group, a 1-methyl propyl group, a 2-methyl propyl group, ann-pentyl group, a 1-ethyl propyl group, a 1-methyl butyl group, a2-methyl butyl group, a 3-methyl butyl group, a 1,1-dimethyl propylgroup, a 1,2-dimethyl propyl group, a 2,2-dimethyl propyl group, acyclopentyl group, an n-hexyl group, a 1-methyl pentyl group, 2-methylpentyl group, a 3-methyl pentyl group, a 4-methyl pentyl group, a1,1-dimethyl butyl group, a 1,2-dimethyl butyl group, a 1,3-dimethylbutyl group, a 2,2-dimethyl butyl group, a 2,3-dimethyl butyl group, a3,3-dimethyl butyl group, a 1-ethyl butyl group, a 2-ethyl butyl group,a cyclohexyl group, a phenyl group, etc. Here, the substituent maycontain atoms other than carbon, such as oxygen, sulfur, nitrogen,silicon, fluorine, bromine, chlorine and iodine.

In the configuration example of FIG. 1( b), the thickness of each layerwithin an area AX which the laser beam enters is, for example, as shownin FIG. 1. That is, in this example, the thickness of the L0 reflectinglayer 106 of Ag or an Ag alloy is selected within a range of 15 nm to 35nm, and the thickness of the L1 reflecting layer 108 of Ag or an Agalloy is selected within a range of 60 nm to 150 nm (i.e., the thicknessof the L1 reflecting layer>the thickness of the L0 reflecting layer).Moreover, the thickness of the intermediate layer 104 is selected withina range of 25±10 μm, and the adhesive layer 103 is managed so that therange of its variation may be 2 μm or less.

FIG. 2 is a diagram showing a concrete example of a metal complexportion of an organic material for the recording layer. A circularperipheral region around the central metal M of the shown azo metalcomplex is a coloring area 8. When the laser beam passes through thiscoloring area 8, localized electrons in this coloring area 8 resonatewith a change of the electric field of the laser beam, and absorb theenergy of the laser beam. When the frequency of the electric fieldchange at which the localized electrons resonate most and easily absorbthe energy is converted to the wavelength of the laser beam, a resultingvalue is indicated by a maximum absorption wavelength λmax. A longerlength of the coloring area 8 (resonance range) as shown in the drawingshifts the maximum absorption wavelength λmax to the longer waveformside. Moreover, the replacement of the atoms of the central metal Mchanges the localization range of the localized electrons around thecentral metal M (how much the central metal M can attract the localizedelectrons to the vicinity of the center), and the value of the maximumabsorption wavelength λmax changes. For example, if a selection is madeso that the λmax may be about 405 nm, an organic material sensitive(light absorption) to a wavelength of 405 nm can be obtained.

As the dye material for the recording layer (e.g., the L0 or L1) havingthe light absorption at a wavelength of 405 nm, an organic dye materialcan be used whose general structural formula is shown in FIG. 2 andwhich has a structure combining an organic metal complex portion anunshown dye material portion. As the central metal M of the organicmetal complex, cobalt or nickel (or, for example, scandium, yttrium,titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium,molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium,osmium, rhodium, iridium, palladium, platinum, copper, silver, gold,zinc, cadmium, mercury, etc.) can be used. Moreover, although not shownin the drawing, cyanine dyes, styryl dyes, monomethinecyanine dyes canbe used as the dye material portion.

Here, a recording principle interpreted in current DVD-R discs will bedescribed. In the current DVD-R disc, when the laser beam is applied tothe recording film, the recording layer locally absorbs the energy ofthe laser beam and have high heat. Beyond a particular temperature, thetransparent substrate locally deforms. While the mechanism which inducesthe deformation of the transparent substrate is different depending onthe manufactures of the DVD-R discs, the causes are said to be:

(1) the local plastic deformation of the transparent substrate due toevaporation energy of the recording layer, and/or

(2) the local plastic deformation of the transparent substrate due toheat transmitted from the recording layer to the transparent substrate.The local plastic deformation caused in the transparent substratechanges the optical distance of the laser beam which returns afterpassing through the transparent substrate, being reflected by the lightreflecting layer and again passing through the transparent substrate. Aphase difference is produced between the laser beam from within therecording mark which returns after passing through the locallyplastically deformed portions of the transparent substrate, and thelaser beam from portions around the recording mark which returns afterpassing through the non-deformed portions of the transparent substrate.Thus, the amount of reflected light changes due to the interferencebetween these laser beams. Moreover, particularly when theabove-mentioned mechanism of (1) is produced, a substantial change of arefractive index n₃₂ caused by the hollowing within the recording markof the recording layer due to evaporation (vaporization), or a change ofthe refractive index n₃₂ caused by the thermal decomposition of theorganic dye recording material within the recording mark alsocontributes to the production of the phase difference. In the currentDVD-R disc, the recording layer has to be at a high temperature (anevaporation temperature of the recording layer in the above-mentionedmechanism of (1), or a temperature in the recording layer needed for theplastic deformation of the transparent substrate in the mechanism of(2)) until the transparent substrate locally deforms, and the recordinglayer also has to be at a high temperature to thermally decompose orevaporate (vaporize) part of the recording layer. Therefore, high powerof the laser beam is needed to form the recording mark.

As the first stage for forming the recording mark, the recording layerhas to be able to absorb the energy of the laser beam. A lightabsorption spectrum in the recording layer greatly influences therecording sensitivity of the organic dye recording film.

FIG. 2 shows a concrete structural formula of a concrete contents “azometal complex+Cu” of the components of the information storage mediumdescribed above. The circular peripheral region around the central metalM of the azo metal complex shown in FIG. 2 is the coloring area 8. Whenthe laser beam passes through this coloring area 8, localized electronsin this coloring area 8 resonate with a change of the electric field ofthe laser beam, and absorb the energy of the laser beam. When thefrequency of the electric field change at which the localized electronsresonate most and easily absorb the energy is converted to thewavelength of the laser beam, a resulting value is referred to as themaximum absorption wavelength, and indicated by λ_(max). A longer lengthof the coloring area 8 (resonance range) as shown in FIG. 2 shifts themaximum absorption wavelength λ_(max) to the longer waveform side.Moreover, the replacement of the atoms of the central metal M in FIG. 2changes the localization range of the localized electrons around thecentral metal M (how much the central metal M can attract the localizedelectrons to the vicinity of the center), and the value of the maximumabsorption wavelength λ_(max) changes.

The optical disc 100 using a dye indicated by a chemical formula in FIG.3 was manufactured, and information recording was performed for randomdata. When an error rate SbER of the L0 layer was measured, 5.4e-6 couldbe obtained which was a satisfactory value lower enough than a targetvalue of 5.0e-5 (higher than a practical level). Further, when arepeated pattern with a 11T mark and a 11T space was recorded and thenplayed back, almost no distortion of a waveform was observed, and adifference between a maximum value and a minimum value of I11L([I11Lmax−I11Lmin]/I11min) which was a space level (when the 11T spacewas played back) was 2%. Here, the length of the 11T mark was 1.12 μm,and 1.2*Na/λ was 0.74 μm, resulting in a sufficiently long mark. WhileIR, MS and NMR before and after recording were analyzed regarding thisdye, no difference was found.

<<General Parameters>>

General parameters of a recordable single-sided dual-layer disc comparedwith a recordable single-sided single-layer disc are shown in FIG. 4.The general parameters of the recordable single-sided dual-layer discare about the same as the general parameters of the single-layer disc,but are different in the following points. In the recordablesingle-sided dual-layer disc, a recording capacity available to a useris 30 GB, the internal radius of a data area is 24.6 mm in the layer 0and 24.7 mm in the layer 1, and the outside radius of the data area is58.1 mm (both in the L0 and the L1).

FIG. 5 is a flowchart explaining a recording method using the opticaldisc according to the one embodiment. Modulated laser having awavelength of, for example, 405 nm is applied to a recording targetlayer (L0 or L1) of the disc 100 from an optical pickup of an unshowndisc drive, thereby recording object data (VOB, etc., in DVDs orHD_DVDs) (ST 100). After the completion of this recording (ST 102Y),management information on the recorded object data (VMG, etc. in DVDs orHD_DVDs) is written in the disc 100 (ST 104), such that one recording isfinished.

FIG. 6 is a flowchart explaining a playback method using the opticaldisc according to the one embodiment. The management information is readby laser having a wavelength of, for example, 405 nm from the disc 100in which the object data and the management information are recorded inthe processing as in FIG. 5 (ST 200). The read management information istemporarily stored in a work memory of an unshown playback device. Thisplayback device plays back the recorded object data with reference toinformation on a playback procedure in the stored managementinformation, etc. (ST 202). This playback terminates when the userinstructs to terminate the playback or when the playback has reached apoint where the playback procedure information within the managementinformation indicates the termination of the playback (ST 204Y).

FIG. 7 is a diagram explaining one example of the layout of physicalsectors in the optical disc 100 in FIG. 1. As shown in FIG. 7, aninformation area provided over the two layers comprises 7 areas: asystem lead-in area, a connection area, a data lead-in area, a dataarea, a data lead-out area, a system lead-out area and a middle area.The middle area is provided in each layer, such that a playback beam canbe moved from the layer 0 (L0) to the layer 1 (L1). The data area DArecords main data (the management information VMG, the object data VOB,etc. in the example of FIG. 1( e)). The system lead-in area SLA includescontrol data, reference codes, etc. The data lead-out area permitssmooth sequential reading.

<<Lead-Out Area>>

The system lead-in area and the system lead-out area include tracksincluding emboss pits. The data lead-in area, the data area and themiddle area in the layer 0 (L0), and the middle area, the data area andthe data lead-out area in the layer 1 (L1) include a groove track. Thegroove track is continuous from the start position of the data lead-inarea to the end position of the middle area in the layer 0, andcontinuous from the start position of the middle area to the endposition of the data lead-out area in the layer 1. In addition, if apair of single-sided dual-layer disc substrates is prepared and bondedtogether, a double-sided four-layer disc having two reading surfaces isproduced.

FIG. 8 is a diagram explaining an example of the configuration of thelead-in area in the optical disc in FIG. 1. As shown in FIG. 8, thesystem lead-in area SLA in the layer 0 (L0) is composed of an initialzone, a buffer zone, a control data zone and a buffer zone in order fromthe inner peripheral side. The data lead-in area in the layer 0 iscomposed of a blank zone, a guard track zone, a drive test zone, a disctest zone, a blank zone, a recording management data (RMD) duplicationzone, an L-RMZ (recording position management data), an R-physicalformat information zone and a reference code zone in order from theinner peripheral side. A start address (inner peripheral side) of thedata area in the layer 0 (L0) is different by a clearance from an endingaddress (inner peripheral side) of the data area in the layer 1, and theending address (inner peripheral side) of the data area in the layer 1(L1) is closer to the outer peripheral side than the start address(inner peripheral side) of the data area in the layer 0.

<<Structure of Lead-In Area>>

FIG. 8 illustrates the structure of the lead-in area in the layer 0(L0). In the system lead-in area, there are arranged, in order from theinner peripheral side, the initial zone, the buffer zone, the controldata zone and the buffer zone. In the data lead-in area, there arearranged, in order from the inner peripheral side, the blank zone, theguard track zone, the drive test zone, the disc test zone, the blankzone, the RMD duplication zone, the recording position management(recording management) zone (L-RMZ) within the data lead-in area, theR-physical format information zone and the reference code zone.

<<Details of System Lead-In Area>>

The initial zone includes an embossed data segment. The main data in adata frame recorded as a data segment of the initial zone is set at“00h”. The buffer zone is constituted of 1024 physical sectors of 32data segments. The main data in a data frame recorded as a data segmentof this zone is set at “00h”. The control data zone includes an embosseddata segment. The data segment includes embossed control data. Thecontrol data is constituted of 192 data segments originating at PSN123904(01 E400h).

An example of the configuration of the control data zone is shown inFIG. 9. Moreover, an example of the configuration of the data segment inthe control data section is shown in FIG. 10. The contents of the firstdata segment in the control data section are repeated sixteen times. Thefirst physical sector in each data segment includes physical formatinformation. The second physical sector in each data segment includesdisc manufacturing information. The third physical sector in each datasegment includes copyright protection information. The contents of theother physical sectors in each data segment serve as reserve areas forsystem use.

FIG. 11 is a diagram explaining one example of the physical formatinformation in the control data section. FIG. 12 is a diagram explainingone example of data area allocation in the physical format information.The contents written in byte positions (BPs) in this physical formatinformation are as follows: values of read power, recording velocities,the reflectance of the data area, push-pull signals and on-track signalsshown from BP132 to BP154 are illustrative. Actual values for these canbe selected by a disc manufacturer from values that satisfy rules foremboss information and rules for characteristics of user data afterrecorded. The contents of the data area allocation written in BP4 toBP15 are as shown in, for example, FIG. 12.

BP149 and BP152 in FIG. 11 specify the reflectance of the data areas inthe layer 0 and the layer 1. For example, 0000 1010b indicates 5%.Actual reflectance is specified by the following equation:

Actual reflectance=value×(½).

BP150 and BP153 specify the push-pull signals of the layer 0 and thelayer 1. In each of these BPs, an unshown bit b7 specifies the shape ofthe track of the disc in each layer, and unshown bits b6 to b0 specifythe amplitudes of the push-pull signals:

Track shape: 0b (track on groove)

-   -   1b (track on land)

Push-pull signal: for example, 010 1000b indicates 0.40.

The actual amplitude of the push-pull signal is specified by thefollowing equation:

Actual amplitude of push-pull signal=value×( 1/100).

BP151 and BP154 specify the amplitudes of the on-track signals in thelayer 0 and the layer 1:

On-track signal: for example, 0100 0110b indicates 0.70.

The actual amplitude of the on-track signal is specified by thefollowing equation:

Actual amplitude of on-track signal=value×( 1/100).

In addition, recording-related parameters of the L0 as illustrated inFIG. 13 can be written in BP512 to BP543 of the physical formatinformation, and information on initial peak power, bias power, etc. inrecording in the L0 layer can be taken from the description in FIG. 13.Moreover, recording-related parameters of the L1 as illustrated in FIG.14 can be written in BP544 to BP2047 of the physical format information,and information on initial peak power, bias power, etc. in recording inthe L1 layer can be taken from the description in FIG. 14.

Explanation of Recording Conditions (Information on Write Strategy)

A recording waveform used when the optimum recording power is examined(exposure conditions during recording) will be described using FIG. 15.Exposure levels during recording include four levels: recording power(peak power), bias power 1, bias power 2, and bias power 3. In forming along recording mark 9 (4T or more), modulation in a multi-pulse form isperformed between the recording power (peak power) and the bias power 3.In this embodiment, the minimum mark length for a channel bit length Tis 2T in both an “H format” and a “B format”. When the minimum mark of2T is recorded, one light pulse at the recording power (peak power)level is used after the bias power 1, and the bias power 2 once comesimmediately after the light pulse, as shown in FIG. 15. When a recordingmark 9 having a length of 3T is recorded, exposure is performed for twolight pulses including a first pulse at the recording power (peak power)level coming after the bias power 1 and a light pulse, and then the biaspower 2 comes once. When a recording mark 9 having a length of 4T ormore is recorded, exposure is performed at multi-pulses and the lightpulse, and the bias power 2 comes.

Vertical broken lines in FIG. 15 indicate channel clock cycles (T). Whenthe minimum mark of 2T is recorded, the pulse rises at a positiondelayed for T_(SFP) from a clock edge, and falls at a position behindT_(ELP) from an edge after one clock. A period immediately thereafter inwhich the bias power 2 comes is defined as T_(LC). The values ofT_(SFP), T_(ELP) and T_(LC) are recorded in physical format informationPFI within a control data zone CDZ in the case of the H format.

In the case of forming a long recording mark 9 of 3T or more, the pulserises at a position delayed for T_(SFP) from the clock edge, and ends ina last pulse. The bias power 2 comes during T_(LC) immediately after thelast pulse, and lag times from the clock edge corresponding to thetimings of the rising/falling of the last pulse are defined as T_(SLP)and T_(ELP). Moreover, time measured from the clock edge correspondingto the timing of the falling of a head pulse is defined as T_(EFP), andthe interval of one multi-pulse is defined as T_(MP).

Each of the interval between T_(ELP) and T_(SFP), the interval ofT_(MP), the interval between T_(ELP) and T_(SLP), and the interval ofT_(LC) is defined by a half value width with respect to the maximumvalue. Further, in this embodiment, set ranges of the parametersdescribed above are:

0.25T≦T _(SFP)≦1.50T  (eq. 01)

0.00T≦T _(ELP)≦1.00T  (eq. 02)

1.00T≦T _(EFP)≦1.75T  (eq. 03)

−0.10T≦T _(SLP)≦1.00T  (eq. 04)

0.00T≦T _(LC)≦1.00T  (eq. 05)

1.50T≦T _(MP)≦0.75T  (eq. 06).

Furthermore, in this embodiment, the values of the parameters describedabove can be changed depending on a mark length and a leading/trailingspace length.

When the optimum recording power of the recordable information recordingmedium for which recording is performed in accordance with the recordingprinciple shown in this embodiment is examined, the values of theparameters including the bias power 1, the bias power 2 and the biaspower 3 are 2.6 mW, 1.7 mW and 1.7 mW, respectively, and playback poweris 0.4 mW.

On the basis of the values, etc. of the parameters calculated asdescribed above, “recording conditions (information on the writestrategy) optimum for a storage medium in a device (drive) in which testwriting has been performed on the storage medium in its drive test zone”can be determined.

Furthermore, the repeated pattern having the 11T mark and the 11T spacehas been used as data for the recording signal in addition to the datadescribed above. Physical formats present on the recording layers (L0and L1) on the transparent resin substrate 101 and the photopolymer 104resin used in the embodiment described above are as described withreference to FIG. 7 to FIG. 15.

FIG. 16 is a diagram explaining the formation of a burst cutting area(BCA) on the L1 layer of the recordable single-sided multilayer(dual-layer) optical disc according to the one embodiment. Here, the L0layer is provided on the substrate 101 on a laser receiving side, the L1layer is provided opposite to the L0 layer, and the substrate 102 isdisposed on the L1 layer, thereby forming the laminated dual-layer disc100 having a substrate thickness of 1.2 mm. The burst cutting area (BCA)in which information unique to the disc is recorded in a bar-code-shapedpattern (mark) is provided on the L1 layer on the inner peripheral sideof the disc 100.

Information unique to the disc is preferably recorded in advance on theindividual optical disc at the time of its manufacture. The informationunique to the disc recorded at this point is used, for example, when theindividual disc has to be identified for copy protection. In opticaldiscs such as a CD, a DVD, a BD, and an HD_DVD, such information (BCArecords, etc.) unique to the disc is inscribed in advance as thebar-code-shaped pattern called the BCA in an inner peripheral portion ofthe disc (see BCAm in FIG. 16). At this point, in the case of aplayback-only dual-layer optical disc, such information is generallyrecorded in a layer located on a far side when viewed from an entrancesurface of recording/playback light.

Recently, single-sided dual-layer optical discs have been developed inrecording-type optical discs rather than the playback-only optical discsin response to a desire for higher capacity in the optical disc. Inorder to be compatible with the playback-only discs, it is alsopreferable in the recording-type dual-layer optical discs that the BCAsignal be recorded in the layer located on the far side when viewed fromthe entrance surface of the recording/playback light. However, there aresome problems associated with this. A method of recording the BCA willbe described below, and the problems in the case of the dual layer willbe mentioned.

One method of providing the BCA in the disc is to inscribe the patternof the BCA in a stamper serving as a mold when the optical disc ismolded. However, the BCA pattern has to be inscribed in the produceddisc by, for example, a laser beam in order to record individual uniqueinformation on each disc. In general, when the BCA is recorded on theplayback-only disc, the pattern is produced by burning off thereflecting film (aluminum, silver, or an alloy thereof) with laser.Moreover, when the BCA is recorded on a phase-change recording disc, thepattern is produced by causing a phase change in the recording film withlaser to change its reflectance.

On the other hand, in the case of the recordable optical disc using theorganic dye material, the sensitivity of the dye is significantly highto the wavelength, so that the BCA pattern can not be satisfactorilyrecorded even if a current BCA recording apparatus which uses laserhaving a long wavelength (e.g., 650 nm, 680 nm or 780 nm) is applied tothe next-generation optical disc (e.g., the BD or HD_DVD) using the dyeconforming to a short wavelength (e.g., 405 nm). In this case, laserpower of the BCA recording apparatus could be strengthened, or the laserwavelength of the BCA recording apparatus could be changed to correspondto a data recording wavelength (e.g., 405 nm). However, since theinformation on the BCA is recorded in the far layer (L1) through thenear layer (L0), the dye of the near layer also reacts in this methodcoupled with the fact that the focal depth of the BCA recordingapparatus is extremely large (or that BCA recording light is parallellight). This results in noise (an interlayer crosstalk signal) duringthe playback of the BCA signal.

Therefore, in this embodiment, an organic metal used is selected so thatthe recording sensitivity to a wavelength B is higher in the far layer(L1) in which the BCA is recorded than in the near layer (L0) in whichthe BCA is not recorded, where A (nm) is a wavelength used for therecording/playback of data, and B is the wavelength of the BCA recordingapparatus. A dye conforming to the wavelength of the BCA recordingapparatus as well is used in the far layer (L1) alone (e.g., two kindsof dyes with difference sensitivities are mix, such as a dye sensitiveto about 405 nm and a dye sensitive to about 650 nm to 780 nm) while awavelength used for the recording of actual data (such ashigh-definition video data encoded by MPEG4AVC) is separated from awavelength used for the recording of the BCA information (A≠B), suchthat the BCA signal can be selectively recorded in the far layer (L1)alone.

This embodiment illustrates a recordable optical disc which has adiameter of 120 mm and a thickness of 1.2 mm (two polycarbonate moldedsubstrates of 0.6 mm bonded together) and which has two recording layersusing the organic dye material. An optical system adapted to awavelength (λ) of 405 nm and a numerical aperture (NA) of 0.65 is usedfor the recording/playback light. An inter-groove track pitch in a datarecording area is, for example, 400 nm, and the position of the BCA areais at, for example, a radius of 22.2 mm to 23.1 mm. Moreover, the BCApattern is formed of a bar-code-shaped pattern having, for example, awidth (in a tangential direction) of several ten μm and a (diametrical)length of about several hundred μm.

In addition, this embodiment is not limited to the illustrationdescribed above. For example, an optical disc whose surface is providedwith a cover layer of 0.1 mm may be used, an optical disc having adiameter of 80 mm may be used, a higher density track pitch pattern maybe used, laser having a shorter wavelength (e.g., λ is 400 nm or less)may be used, and an optical system (objective lens) adapted to a highernumerical aperture (e.g., an NA of 0.8 to 0.9) may be used.

Concrete examples of materials for the recordable multilayer opticaldisc according to the one embodiment are as follows: polycarbonate forthe molded substrates; nickel (N1) for the stamper used for molding; anorganic dye material made of an azo, diazo, cyanine, phthalocyanine orstyryl based substance or a mixture of these substances for therecording layers; silver (Ag), aluminum (Al) or gold (Au), or a metalliccompound based on these substances for the reflecting film; and anacrylic or epoxy ultraviolet curing resin for an adhesive. Thesematerials are not limited to the above-mentioned illustrations either.However, the embodiments concern a recordable optical disc having aplurality of recording layers, and a manufacturing method, etc. will bedescribed later with reference to FIG. 21 regarding the recordablesingle-sided dual-layer optical disc as an example of the recordableoptical disc.

In addition, the case has been described in the example of the aboveembodiment where the BCA is formed on the L1 layer through the L0 layer.However, when the reflecting layer having the dimensions andconfiguration as illustrated in FIG. 1 is provided, the material of theL1 layer is selected to correspond to the power of the laser used andits wavelength (it can be selected by trial and error) such that thelaser for the BCA can be applied through the dummy substrate 102 (from adummy substrate side disc surface opposite to the surface in the exampledescribed above) to post-cut the BCA information. Part of the L1 layeris deformed or changed by the laser applied through the dummy substrate102, where the BCA information (the BCA mark in FIG. 16 or the BCArecord in FIGS. 17A and 17B) can be post-cut.

FIGS. 17A and 17B are diagrams explaining an example of contents of theBCA record recorded in the BCA in FIG. 16. As illustrated in FIG. 17A,there are written, in this record, a BCA record ID (indicating an HD_DVDbook type identifier) at relative byte positions 0 to 1, a versionnumber of an applied standard at a relative byte position 2, a datalength at a relative byte position 3, a book type and a disc type of awritten standard at a relative byte position 4, and an extended partversion at a relative byte position 5, and relative byte positions 6 to7 are reserved for writing other information.

Sections for the book type and the disc type of the written standardwith which the disc is compliant in the BCA record is as illustrated inFIG. 17B. That is, information indicating a standard for the HD_DVD-Rcan be written in the book type, and a mark polarity flag and a twinformat flag can be written in the disc type.

The mark polarity flag in FIG. 17B can indicate during “0b” that thedisc is a “Low-to-High” disc in which a signal from the recording markis larger than a signal from a space (between the adjacent marks), andcan indicate during “1b” that the disc is a “High-to-Low” disc in whichthe signal from the recording mark is smaller than the signal from thespace. Moreover, the twin format flag can indicate during “0b” that thedisc is not a twin format disc, and can indicate during “1b” that thedisc is a twin format disc. When the disc is a twin format disc, thedisc (on which the BCA record is recorded) has two recording layers, andthe respective layers have individual formats (e.g., an HD_DVD-Videoformat and an HD_DVD-Video Recording format) set in the DVD forum.

There is no twin format disc in current DVDs, but there can be a twinformat disc in the next-generation HD_DVD, so that being able to writethe twin format flag in the BCA means much for the recordable multilayer(dual-layer) optical disc according to the one embodiment (anext-generation disc for the HD_DVD).

FIG. 18 is a diagram explaining an example of the configuration of adevice for recording specific information including the BCA record, etc.in FIGS. 17A and 17B in the BCA. The recording of the BCA signal (asignal including information such as the BCA record in FIGS. 17A and17B) by the BCA recording apparatus is carried out for the disc 100 in acompleted form. Laser 210 is modulated in accordance with the BCA signalfrom a controller 202, and the bar-code-shaped BCA mark is recordedsynchronously with the rotation of the disc 100. One of the laserwavelengths ranging from 600 nm to 800 nm (650 nm to 780 nm or 680 nm to780 nm in general) is employed as the laser wavelength of the BCArecording apparatus. In the case of the dual-layer optical disc, arecording place of the BCA is generally located at a radius of about22.2 mm to 23.1 mm of the inner peripheral portion of the L1 layer.While the laser is applied to the L1 layer through the L0 layer in thecase of the BCA recording, the optical absorptance (sensitivity) isadjusted to a wavelength of 650 nm to 780 nm (or 680 nm to 780 nm) inthis embodiment (the sensitivity of the L1 layer>the sensitivity of theL0 layer). Therefore, in a practical sense, the BCA signal can beselectively recorded in the L1 layer alone with accuracy.

Thus, the sensitivity (the optical absorptance in the used wavelength)of the dye of each layer is adjusted, such that the BCA signal can berecorded in the next-generation optical disc without any change in thelaser wavelength and laser power of the BCA recording apparatusgenerally used in DVD production lines at present (the laser power isproperly increased depending on the situation). Moreover, since the BCAsignal can be selectively recorded in the L1 layer alone, there is noextra crosstalk noise from the L0 layer during playback.

That is, in the one embodiment, the sensitivity of the dye of each layer(such as the L0 or L1) is adjusted (e.g., an organic metal is used suchthat the sensitivity or optical absorptance of the dye of the L1 layerat 600 nm to 800 nm or 650 nm to 780 nm or 680 nm to 780 nm is higherthan the sensitivity or optical absorptance of the dye of the L0 layer).Thus, the BCA signal can be recorded in the next-generation optical disc(such as a single-sided dual-layer HD_DVD-R) without any change in thelaser wavelength and laser power of the BCA recording apparatusgenerally used in the DVD production lines at present. At that point,since the BCA information can be selectively recorded in the L1 layeralone, no extra crosstalk noise from the L0 layer is mixed during theplayback of the BCA signal.

Furthermore, the BCA information can also be selectively recorded in theL1 layer alone when the laser for the BCA is applied through the dummysubstrate 102 to post-cut the BCA information, so that no extracrosstalk noise from the L0 layer is mixed during the playback of theBCA signal.

FIG. 19 is a flowchart explaining one example of a procedure forrecording (BCA post-cut) the specific information in the L1 layer of therecordable single-sided multilayer (dual-layer) optical disc in FIG. 16.When the BCA signal including the specific information such as the BCArecord in FIGS. 17A and 17B is supplied to a laser output controller 208from the controller 202 in FIG. 18, laser beam pulses having one of thewavelengths 600 nm to 800 nm (650 nm to 780 nm, or 680 nm to 780 nm) areemitted from the laser diode 210 in correspondence with the contents ofthe signal (ST10). The laser beam pulses thus emitted are applied to theBCA recording place in the L1 layer through the L0 layer of the disc 100shown in FIG. 16 (or through the dummy substrate 102) (ST12). Thisapplication is continued synchronously with the rotation of the disc100. When there is no more remaining information to be recorded in theBCA (YES in ST14), the BCA post-cut in the L1 layer through the L0 layerterminates.

FIG. 20 is a flowchart explaining one example of a procedure for playingback the specific information (such as the BCA record) from the L1 layerof the recordable single-sided multilayer (dual-layer) optical disc inFIG. 16. When the information recorded in the BCA is played back, thelaser beam having a predetermined wavelength (e.g., 405 nm or 650 nm) isapplied to the BCA of the L1 layer through the L0 layer (ST20). Thespecific information on the optical disc (such as the BCA record inFIGS. 17A and 17B) is read from the reflected light (ST22). The readingis continued synchronously with the rotation of the disc 100. When thereis no more remaining information to be read from the BCA (YES in ST24),the BCA playback from the L1 layer through the L0 layer terminates.

FIG. 21 is a diagram explaining an example of a process of manufacturingthe recordable single-sided dual-layer optical disc according to the oneembodiment. A method of manufacturing this recordable dual-layer opticaldisc will be described below along with FIG. 21. First, a molding platefor the L0 layer is manufactured by injection molding (block 0301). Amolding material is generally polycarbonate. The stamper used as a moldfor molding the L0 layer is manufactured by Ni plating from aphotoresist pattern exposed to the laser. The dimensions of the moldingplate include a diameter of 120 mm, an inside diameter of 15 mm and athickness of 0.6 mm. An organic dye material serving as the recordinglayer is applied to this molding plate by a known spin coat method, anda metal film (e.g., silver of a silver alloy) serving as the reflectingfilm is formed by, for example, a known sputter method (block 0302). Inaddition, this L0 layer is semitransparent to allow the transmission ofthe laser beam.

In parallel with this, a plastic stamper serving as a mold for the L1layer is similarly manufactured by injection molding (block 0303). Amolding material is generally cycloolefin polymer, but may also be, forexample, polycarbonate or acrylic. An N1 stamper for the L1 layer issimilarly manufactured by plating with a photoresist exposed to thelaser, but the concavity and convexity of the pattern are reverse tothose in the L0 layer.

The molding plate of the L0 layer in which the recording layer is formedis bonded to the plastic stamper via a photopolymer, and they are curedby the application of ultraviolet rays (block 0304). Then, the plasticstamper is peeled off to bare the photopolymer layer on which the L1layer pattern is transferred (block 0305). Next, an organic dye materialserving as the recording layer is applied onto photopolymer in the L1layer by the spin coat method, and a metal film (e.g., silver of asilver alloy) serving as the reflecting film is formed by, for example,the sputter method (block 0306).

In parallel with this, a dummy plate (the material of which is, forexample, polycarbonate) is manufactured by injection molding (block0307), and this dummy plate is bonded by an ultraviolet curing adhesive,thereby completing the recordable dual-layer optical disc (block 0308).In addition, although not shown in the drawing, the dummy plate may besubjected to surface coating for printing by user using, for example, aninkjet printer, or a pattern of, for example, a brand name of the discmanufacturer (or seller) or a product name may be added to the dummyplate.

The dimensions of each layer of the recordable multilayer (dual-layer)R-disc 100 finished in the manner are, for example, as shown in FIG. 1.

In carrying out the embodiments, the material and thickness of the lightreflecting layer 108 included in the second recording part (L1) have tobe properly set to strictly control the reflection amount of incidentlight. It is preferable that the thickness of this light reflectinglayer (Ag or an Ag alloy) 108 be generally 60 nm to 150 nm. Below 60 nm,the amount of light transmission in the light reflecting layer increasesto cause difficulty in obtaining a sufficient amount of reflected light.Then, the gain of a servo detection signal such as a push-pull signalbecomes insufficient, which causes difficulty in stablerecording/playback. On the other hand, beyond 150 nm, the amount ofreflected light increases to an excessive degree, and the influence ofthe interlayer crosstalk becomes unallowable, leading to significantdeterioration in the characteristics of the recording/playback signal.

This will be more concretely described below. When recording/playback isperformed in the recording layer 105 of the first recording part (L0),part of the recording/playback light which has passed through the lightreflecting layer 106 included in the first recording part (L0) isreflected by the light reflecting layer 108 included in the secondrecording part (L1), and returns to the first recording part (L0). Atthis point, in the case where the reflectance of the light reflectinglayer 108 included in the second recording part (L1) is high,unnecessary signal components increase when recording/playback isperformed in the recording layer 105 of the first recording part (L0),which becomes a factor for significant deterioration in the quality ofthe recording/playback signal for the first recording part (L0).

Furthermore, because the interlayer crosstalk is greatly influenced bythe amounts of reflected light in the first recording part (L0) and thesecond recording part (L1), a recording position has to be strictlycontrolled to always carry out stable recording/playback (see theparameters, etc. in FIG. 4).

In addition, it is preferable that the thickness of the light reflectinglayer (semi-transmissive reflecting layer using Ag or an Ag alloy) 106included in the first recording part (L0) be generally 15 nm to 35 nm.Below 15 nm, the amount of light transmission in the light reflectinglayer increases to cause difficulty in obtaining a sufficient amount ofreflected light. Then, the gain of the servo detection signal such asthe push-pull signal becomes insufficient, which causes difficulty instable recording/playback. At the same time, the influence of theinterlayer crosstalk due to the light reflected by the light reflectinglayer 108 included in the second recording part (L1) reaches anunallowable level, and the characteristics of the recording/playbacksignal significantly deteriorate. On the other hand, beyond 35 nm, theamount of reflected light increases to an excessive degree. Then, thegain of the servo detection signal such as the push-pull signalincreases, so that the recording/playback is possible, but therecording/playback in the recording layer 107 of the second recordingpart (L1) is difficult because of a decrease in optical transmittance.

EXAMPLE 1a

The thickness of the light reflecting layer 106 of the L0 is 25 nm, andthe thickness of the light reflecting layer 108 of the L1 is 100 nm (thethickness of the L1 reflecting layer>the thickness of the L0 reflectinglayer), in which case an optimum reflection amount can be obtained, andthe interlayer crosstalk can be reduced. At the same time, BCA recordingthrough the dummy substrate 102 can be stably carried out, and asufficient signal modulation factor can be obtained in this BCArecording.

EXAMPLE 2a

The thickness of the light reflecting layer 106 of the L0 is 20 nm, andthe thickness of the light reflecting layer 108 of the L1 is 80 nm (thethickness of the L1 reflecting layer>the thickness of the L0 reflectinglayer), in which case an optimum reflection amount can be obtained andthe interlayer crosstalk can be reduced likewise. At the same time, BCArecording through the dummy substrate 102 can be stably carried out, anda sufficient signal modulation factor can be obtained in this BCArecording.

EXAMPLE 1b

When the thickness of the light reflecting layer 108 of the L1 is 100nm, an optimum reflection amount can be obtained, and the interlayercrosstalk can be reduced. At the same time, BCA recording through thedummy substrate 102 can be stably carried out, and a sufficient signalmodulation factor can be obtained.

EXAMPLE 2b

The light reflecting layer 108 of the L1 is manufactured as in Example1b, and the quality of the playback signal in the system lead-out area(a right area shown in FIG. 7) is evaluated. As a result, it has beenconfirmed that a sufficient signal modulation factor can be obtained.

EXAMPLE 1c

The thickness of the light reflecting layer 106 of the L0 is 25 nm, thethickness of the light reflecting layer 108 of the L1 is 100 nm, and thethickness of the intermediate layer 104 over the entire surface of thedisc is 27 μm±2 μm (a more concrete example of a range of 25±10 μm), inwhich case an optimum reflection amount can be obtained, and theinterlayer crosstalk can be reduced. At the same time, BCA recordingthrough the dummy substrate 102 can be stably carried out, and asufficient signal modulation factor can be obtained.

EXAMPLE 2c

The thickness of the light reflecting layer 106 of the L0 is 20 nm, thethickness of the light reflecting layer 108 of the L1 is 80 nm, and thethickness of the intermediate layer over the entire surface of the discis 27 μm±2 μm, in which case an optimum reflection amount can beobtained, and the interlayer crosstalk can be reduced. At the same time,BCA recording through the dummy substrate 102 can be stably carried out,and a sufficient signal modulation factor can be obtained.

COMPARATIVE EXAMPLE 1a Ground 1 that the Thickness of the ReflectingLayer 106 of the L0 is 15 nm or More and 35 nm or Less

The thickness of the light reflecting layer 106 of the L0 is increasedto 40 nm, and the thickness of the light reflecting layer 108 of the L1is 200 nm, in which case the amount of light transmitted to the L1decreases. Therefore, the gain of the unrecorded servo signal at thetime of recording in the L1 is significantly decreased, and stablerecording/playback is difficult. At the same time, BCA recording throughthe dummy substrate is difficult, and a signal modulation factor in theBCA recording part is decreased, so that a sufficient signal quality cannot be obtained.

COMPARATIVE EXAMPLE 2a Ground 2 that the Thickness of the ReflectingLayer 106 of the L0 is 15 nm or More and 35 nm or Less

The thickness of the light reflecting layer 106 of the L0 is increasedto 40 nm, and the thickness of the light reflecting layer 108 of the L1is 100 nm, in which case the amount of light transmitted to the L1 againdecreases. Therefore, the gain of the unrecorded servo signal at thetime of recording in the L1 is significantly decreased, and stablerecording/playback is difficult.

COMPARATIVE EXAMPLE 3a Ground 3 that the Thickness of the ReflectingLayer 106 of the L0 is 15 nm or More and 35 nm or Less

The thickness of the light reflecting layer 106 of the L0 is decreasedto 13 nm, and the thickness of the light reflecting layer 108 of the L1is 100 nm, in which case the transmission of light to the L1 increases,and the reflection of light from the recording layer of the L1 increasesat the same time. As a result, unnecessary signal components increaseduring the recording/playback in the recording layer of the L0, and thecharacteristics of the L0 deteriorate.

COMPARATIVE EXAMPLE 1b Ground 1 that the Thickness of the ReflectingLayer 108 of the L1 is 60 nm or More and 150 nm or Less

When the thickness of the light reflecting layer 108 of the L1 is largerthan 150 nm, the amount of reflection in this light reflecting layer 108increases, and the interlayer crosstalk increases, so that the qualityof a signal in the recording layer 105 of the L0 tends to significantlydeteriorate. At the same time, BCA recording through the dummy substrate102 is difficult, and a signal modulation factor in the BCA recordingpart decrease, so that a sufficient signal quality can not be obtainedfor the BCA information (150 nm is considered a practical upper limit,and 100 nm or less is practically preferable).

COMPARATIVE EXAMPLE 2b Ground 2 that the Thickness of the ReflectingLayer 108 of the L1 is 60 nm or More and 150 nm or Less

When the thickness of the light reflecting layer 108 of the L1 isdecreased to 50 nm, the amount of reflected light in the L1 decreases,so that the gain of the unrecorded servo signal is significantlydecreased, and stable recording/playback is difficult.

COMPARATIVE EXAMPLE 3b Ground that the Thickness of the Reflecting Layer106 of the L0 has to be 15 nm or More

When the thickness of the light reflecting layer 106 of the L0 is 13 nm,the transmission of light to the L1 increases, so that the reflection oflight from the recording layer 107 of the L1 increases, unnecessarysignal components increase during the recording/playback in therecording layer 106 of the L0, resulting in deterioration in therecording/playback characteristics of the L0.

COMPARATIVE EXAMPLE 1c Ground 1 that the Thickness of the IntermediateLayer 104 is 25 μm±10 μm

The thickness of the light reflecting layer 106 of the L0 is 25 nm, thethickness of the light reflecting layer 108 of the L1 is 100 nm, and thethickness of the intermediate layer 104 over the entire surface of thedisc is 35 μm±2 μm, in which case the distance from the laser receivingsurface of the disc 100 to the L1 increases, so that the spot shape ofthe recording/playback laser beam becomes unclear, and therecording/playback signal deteriorates, with the result that stablerecording/playback tends to be difficult (35 μm is considered apractical upper limit).

COMPARATIVE EXAMPLE 2c Ground 2 that the Thickness of the IntermediateLayer 104 is 25 μm±10 μm

The thickness of the light reflecting layer 106 of the L0 is 25 nm, thethickness of the light reflecting layer 108 of the L1 is 100 nm, and thethickness of the intermediate layer 104 over the entire surface of thedisc is 15 μm±2 μm, in which case the distance from the laser receivingsurface of the disc 100 to the L1 decreases, so that the spot shape ofthe recording/playback laser beam becomes unclear, and therecording/playback signal deteriorates, with the result that stablerecording/playback tends to be difficult (15 μm is considered apractical lower limit).

COMPARATIVE EXAMPLE 3c Ground that the Thickness of the Reflecting Layer106 of the L0 is 15 nm or More Even when the Thickness of theIntermediate Layer 104 is 25±10 μm

The thickness of the light reflecting layer 106 of the L0 is decreasedto 13 nm, the thickness of the light reflecting layer 108 of the L1 is100 nm, and the thickness of the intermediate layer 104 over the entiresurface of the disc is 25 μm±2 μm, in which case the transmission oflight to the L1 increases. At this same time, the reflection of lightfrom the reflecting layer 108 of the L1 increases, unnecessary signalcomponents increase during the recording/playback in the recording layer105 of the L0, resulting in deterioration in the characteristics of theL0. That is, in the embodiment of the configuration as shown in FIG. 1,the selection of the thickness of the reflecting layer 106 of the L0 isseverer than the selection of the thickness of the intermediate layer104.

When any one of the embodiments is carried out to adjust the material ofthe reflecting film and the thickness of the reflecting film in theoptical recording medium having two or more recording layers, theinterlayer crosstalk between the first recording layer and the secondrecording layer is reduced, and stable and high-quality recordingcharacteristics can be obtained. Further, the BCA recording can bestably performed in the second recording layer through the dummysubstrate, and a sufficient BCA signal modulation factor can beobtained.

In addition, this invention is not limited to the embodiments describedabove, and various modifications can be made without deviating from thespirit thereof on the basis of technology available at the time in acurrent or future execution phase. For example, the embodiments can becarried out for a single-sided optical disc having three or more layersand even for an optical disc using short-wavelength laser at awavelength of 400 nm or less. Moreover, a suitable combination of theembodiments may be carried out as much as possible in which casecombined effects can be obtained. Further, the embodiments describedabove include inventions at various stages, and suitable combinations ofa plurality of disclosed constitutional requirements permit variousinventions to be extracted. For example, even when some of all theconstitutional requirements shown in the embodiments are eliminated, aconfiguration in which those constitutional requirements are eliminatedcan be extracted as an invention.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

1. An optical recording medium comprising: a first recording part whichincludes a first recording layer where information isrecorded/reproduced by light at a predetermined wavelength and a firstlight reflecting layer and which is disposed on a side closer to asurface receiving the light; and a second recording part which includesa second recording layer where information is recorded/reproduced by thelight and a second light reflecting layer and which is disposed on aside farther from the surface receiving the light than the firstrecording part, the first recording part and the second recording partbeing stacked in a traveling direction of the light, wherein thethickness of the second light reflecting layer is larger than thethickness of the first light reflecting layer.
 2. The optical recordingmedium according to claim 1, wherein the thickness of the second lightreflecting layer is 60 nm or more and 150 nm or less.
 3. The opticalrecording medium according to claim 1, wherein the thickness of thefirst light reflecting layer is 15 nm or more and 35 nm or less.
 4. Theoptical recording medium according to claim 1, wherein the secondrecording part includes a part which deforms or changes by theapplication of light.
 5. The optical recording medium according to claim1, wherein the first light reflecting layer and/or the second lightreflecting layer contains an Ag alloy.
 6. A recording method using anoptical recording medium comprising: a first recording part whichincludes a first recording layer where information isrecorded/reproduced by light at a predetermined wavelength and a firstlight reflecting layer and which is disposed on a side closer to asurface receiving the light; and a second recording part which includesa second recording layer where information is recorded/reproduced by thelight and a second light reflecting layer and which is disposed on aside farther from the surface receiving the light than the firstrecording part, the first recording part and the second recording partbeing stacked in a traveling direction of the light, the thickness ofthe second light reflecting layer being larger than the thickness of thefirst light reflecting layer, the recording method comprising recordinginformation in the first recording part and/or the second recordingpart.
 7. A reproducing method using an optical recording mediumcomprising: a first recording part which includes a first recordinglayer where information is recorded/reproduced by light at apredetermined wavelength and a first light reflecting layer and which isdisposed on a side closer to a surface receiving the light; and a secondrecording part which includes a second recording layer where informationis recorded/reproduced by the light and a second light reflecting layerand which is disposed on a side farther from the surface receiving thelight than the first recording part, the first recording part and thesecond recording part being stacked in a traveling direction of thelight, the thickness of the second light reflecting layer being largerthan the thickness of the first light reflecting layer, the reproducingmethod comprising reproducing information from the first recording partand/or the second recording part.